A conventional bladder has a flexible bladder body disposed inside an unvulcanized tire which is placed inside a vulcanizing mold and expands so that the unvulcanized tire becomes pressure contact with the inner surface of the vulcanizing mold. The outer peripheral surface of the bladder body is provided with a plurality of air release grooves so that the remaining air between the outer surface of the bladder body and the inner surface of the tire can be discharged.    Patent Document 1: Japanese Patent publication No. 2007-83656